Method and apparatus for avoiding circuit-switched call drop in mobile communications

ABSTRACT

Various solutions for avoiding circuit-switched call drop with respect to user equipment and network apparatus in mobile communications are described. An apparatus may transmit a non-access stratum (NAS) message in a NAS signaling connection. The apparatus may receive a NAS response message. The apparatus may initiate a timer to control the NAS signaling connection. The apparatus may further receive a circuit-switched (CS) service notification. The apparatus may stop the timer and execute a CS service procedure.

CROSS REFERENCE TO RELATED PATENT APPLICATION(S)

The present disclosure is part of a non-provisional application claimingthe priority benefit of U.S. Patent Application No. 62/514,032, filed on2 Jun. 2017, the content of which is incorporated by reference in itsentirety.

TECHNICAL FIELD

The present disclosure is generally related to mobile communicationsand, more particularly, to avoiding circuit-switched call drop withrespect to user equipment and network apparatus in mobilecommunications.

BACKGROUND

Unless otherwise indicated herein, approaches described in this sectionare not prior art to the claims listed below and are not admitted asprior art by inclusion in this section.

There are various well-developed and well-defined cellularcommunications technologies in telecommunications that enable wirelesscommunications using mobile terminals, or user equipment (UE). Forexample, the Global System for Mobile communications (GSM) is awell-defined and commonly used communications system, which uses timedivision multiple access (TDMA) technology, which is a multiplex accessscheme for digital radio, to send voice, video, data, and signalinginformation (such as a dialed telephone number) between mobile phonesand cell sites. The CDMA2000 is a hybrid mobile communications 2.5G/3G(generation) technology standard that uses code division multiple access(CDMA) technology. The UMTS (Universal Mobile Telecommunications System)is a 3G mobile communications system, which provides an enhanced rangeof multimedia services over the GSM system. The Long-Term Evolution(LTE), as well as its derivatives such as LTE-Advanced and LTE-AdvancedPro, is a standard for high-speed wireless communication for mobilephones and data terminals. In addition, there are some newly developednext generation communication technologies such as 5^(th) Generation(5G), New Radio (NR), Internet of Things (IoT) and Narrow Band Internetof Things (NB-IoT). These communication technologies are developed forhigher speed transmission and serving for huge number of devicesincluding machine type devices.

In some communication systems, in order to perform a non-access stratum(NAS) signaling procedure, the UE may need to establish a NAS signalingconnection with the network apparatus. When the NAS signaling procedureis finished, it is supposed that there is no other data needed fortransmission. Then, the UE should be waiting for the network apparatusto release the signaling connection or the UE should locally release thesignaling connection. However, during the period of waiting forsignaling connection release, there may be a mobile-terminated (MT)circuit-switched (CS) call coming. It is not clear how the UE shoulddeal with the incoming MT CS call since the signaling connection isgoing to be released.

Accordingly, it is important for the UE to properly deal with theconflict between the incoming MT CS call and the release of thesignaling connection. Therefore, in developing communication systems, itis needed to provide proper mechanisms for arbitrating such conflict.

SUMMARY

The following summary is illustrative only and is not intended to belimiting in any way. That is, the following summary is provided tointroduce concepts, highlights, benefits and advantages of the novel andnon-obvious techniques described herein. Select implementations arefurther described below in the detailed description. Thus, the followingsummary is not intended to identify essential features of the claimedsubject matter, nor is it intended for use in determining the scope ofthe claimed subject matter.

An objective of the present disclosure is to propose solutions orschemes that address the aforementioned issues pertaining to avoidingcircuit-switched call drop with respect to user equipment and networkapparatus in mobile communications.

In one aspect, a method may involve an apparatus transmitting anon-access stratum (NAS) message in a NAS signaling connection. Themethod may also involve the apparatus receiving a NAS response message.The method may further involve the apparatus initiating a timer tocontrol the NAS signaling connection. The method may further involve theapparatus receiving a circuit-switched (CS) service notification. Themethod may further involve the apparatus stopping the timer andexecuting a CS service procedure.

In one aspect, an apparatus may comprise a transceiver capable ofwirelessly communicating with a plurality of nodes of a wirelessnetwork. The apparatus may also comprise a processor communicativelycoupled to the transceiver. The processor may be capable of transmittinga non-access stratum (NAS) message in a NAS signaling connection. Theprocessor may also be capable of receiving a NAS response message. Theprocessor may further be capable of initiating a timer to control theNAS signaling connection. The processor may further be capable ofreceiving a circuit-switched (CS) service notification. The processormay further be capable of stopping the timer and executing a CS serviceprocedure.

It is noteworthy that, although description provided herein may be inthe context of certain radio access technologies, networks and networktopologies such as Long-Term Evolution (LTE), LTE-Advanced, LTE-AdvancedPro, 5th Generation (5G), New Radio (NR), Internet-of-Things (IoT) andNarrow Band Internet of Things (NB-IoT), the proposed concepts, schemesand any variation(s)/derivative(s) thereof may be implemented in, forand by other types of radio access technologies, networks and networktopologies. Thus, the scope of the present disclosure is not limited tothe examples described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of the present disclosure. The drawings illustrate implementationsof the disclosure and, together with the description, serve to explainthe principles of the disclosure. It is appreciable that the drawingsare not necessarily in scale as some components may be shown to be outof proportion than the size in actual implementation in order to clearlyillustrate the concept of the present disclosure.

FIG. 1 is a diagram depicting an example scenario under schemes inaccordance with implementations of the present disclosure.

FIG. 2 is a diagram depicting an example scenario under schemes inaccordance with implementations of the present disclosure.

FIG. 3 is a diagram depicting an example scenario under schemes inaccordance with implementations of the present disclosure.

FIG. 4 is a diagram depicting an example scenario under schemes inaccordance with implementations of the present disclosure.

FIG. 5 is a diagram depicting an example scenario under schemes inaccordance with implementations of the present disclosure.

FIG. 6 is a block diagram of an example communication apparatus and anexample network apparatus in accordance with an implementation of thepresent disclosure.

FIG. 7 is a flowchart of an example process in accordance with animplementation of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED IMPLEMENTATIONS

Detailed embodiments and implementations of the claimed subject mattersare disclosed herein. However, it shall be understood that the disclosedembodiments and implementations are merely illustrative of the claimedsubject matters which may be embodied in various forms. The presentdisclosure may, however, be embodied in many different forms and shouldnot be construed as limited to the exemplary embodiments andimplementations set forth herein. Rather, these exemplary embodimentsand implementations are provided so that description of the presentdisclosure is thorough and complete and will fully convey the scope ofthe present disclosure to those skilled in the art. In the descriptionbelow, details of well-known features and techniques may be omitted toavoid unnecessarily obscuring the presented embodiments andimplementations.

Overview

Implementations in accordance with the present disclosure relate tovarious techniques, methods, schemes and/or solutions pertaining toavoiding circuit-switched call drop with respect to user equipment andnetwork apparatus in mobile communications. According to the presentdisclosure, a number of possible solutions may be implemented separatelyor jointly. That is, although these possible solutions may be describedbelow separately, two or more of these possible solutions may beimplemented in one combination or another.

FIG. 1 illustrates an example scenario 100 under schemes in accordancewith implementations of the present disclosure. Scenario 100 involves auser equipment (UE) 110 and a network apparatus 120, which may be a partof a wireless communication network (e.g., a Long Term Evolution (LTE)network, a LTE-Advanced network, a LTE-Advanced Pro network, a 5thGeneration (5G) network, a New Radio (NR) network, an Internet of Things(IoT) network or a Narrow Band Internet of Things (NB-IoT) network). Inorder to perform a non-access stratum (NAS) signaling procedure, UE 110may need to establish a NAS signaling connection with network apparatus120. UE 110 may be configured to initiate an attach procedure such as acombined evolved packet system (EPS)/international mobile subscriberidentity (IMSI) attach procedure. After the attach procedure, a NASsignaling connection may be established between UE 110 and networkapparatus 120. UE 110 may be in a connected state or a connected mode.

UE 110 may be configured to initiate a tracking area update (TAU)procedure. UE 110 may transmit a tracking area update (TAU) requestmessage without an active flag to network apparatus 120. After receivingthe TAU request, network apparatus 120 may accept the request andtransmit a TAU accept message to UE 110. UE 110 may further transmit aTAU complete message to network apparatus 120 to finish the TAUprocedure. The active flag may be used to indicate whether any otherdata needs to be transmitted after the TAU procedure. In an event thatUE 110 does not indicate the active flag in the TAU request message, itmeans that UE 110 has no data needed to be transmitted. Networkapparatus 120 may further indicate UE 110 to start a timer to controlthe established NAS signaling connection in the TAU accept message.After receiving the TAU accept message, UE 110 may further be configuredto initiate a timer T3440. The timer value of the timer T3440 may beconfigured, for example and without limitation, 10 seconds. The timerT3440 may be configured to control release of the signaling connection.Since there is no data for transmission, UE 110 may initiate the timerT3440 to wait for release of the signaling connection initiated bynetwork apparatus 120. If network apparatus 120 does not release thesignaling connection, UE 110 should locally release the signalingconnection.

Before expiration of the timer T3440, there may be a mobile-terminated(MT) CS call coming. Network apparatus 120 may transmit a CS servicenotification message to inform UE 110 the incoming MT CS call. However,since the timer T3440 is still running, UE 110 is waiting for release ofthe signaling connection from network apparatus 120 or expiration of thetimer T3440 to local release the signaling connection. UE 110 may beconfigured to discard the CS service notification message or any CSpaging. At this stage, no MT circuit-switched fallback (CSFB) will beperformed. When the timer T3440 expires, UE 110 may be configured tolocal release the signaling connection with network apparatus 120. Sincethe signaling connection is released, the MT CS call may be dropped orfailed. UE 110 may enter into an idle mode. The peer end may only haveto re-initiate a second CS call. Network apparatus may only send apaging message to UE 110 for the second CS call. Accordingly, in view ofthe UE behaviors when the timer T3440 is running, MT CS service callsmay suffer failure or delay even when the UE is in a connected state.

FIG. 2 illustrates an example scenario 200 under schemes in accordancewith implementations of the present disclosure. Scenario 200 involves aUE 210 and a network apparatus 220, which may be a part of a wirelesscommunication network (e.g., a Long Term Evolution (LTE) network, aLTE-Advanced network, a LTE-Advanced Pro network, a 5th Generation (5G)network, a New Radio (NR) network, an Internet of Things (IoT) networkor a Narrow Band Internet of Things (NB-IoT) network). In order toperform a NAS signaling procedure, UE 210 may need to establish a NASsignaling connection with network apparatus 220. UE 210 may beconfigured to initiate an attach procedure such as a combined EPS/IMSIattach procedure. After the attach procedure, a NAS signaling connectionmay be established between UE 210 and network apparatus 220. UE 210 maybe in a connected state or a connected mode.

UE 210 may be configured to initiate a NAS signaling procedure. UE 210may transmit a NAS message (e.g., a TAU request message without anactive flag) to network apparatus 220. After receiving the NAS message,network apparatus 220 may accept the request and transmit a NAS responsemessage (e.g., a TAU accept message) to UE 210. UE 210 may furthertransmit a TAU complete message to network apparatus 220 to finish theTAU procedure. Network apparatus 220 may indicate UE 210 to start atimer to control the established NAS signaling connection in the TAUaccept message. After receiving the TAU accept message, UE 210 mayfurther be configured to initiate a timer T3440. The timer value of thetimer T3440 may be configured, for example and without limitation, 10seconds. The timer T3440 may be configured to control release of thesignaling connection. Since there is no data for transmission, UE 210may initiate the timer T3440 to wait for release of the signalingconnection initiated by network apparatus 220. If network apparatus 220does not release the signaling connection, UE 210 should locally releasethe signaling connection.

Before expiration of the timer T3440, there may be a MT CS call coming.Network apparatus 220 may transmit a CS service notification message toinform UE 210 the incoming MT CS call. According to implementations ofthe present disclosure, after receiving the CS service notificationmessage, UE 210 may be configured to stop the timer T3440 and re-use theexisting NAS signaling connection to execute the CS service procedure.Specifically, UE 210 may be configured to perform a CSFB procedure tofallback to a CS service network to execute the CS service procedure.Accordingly, UE 210 may be able to take the MT CS call by using theexisting signaling connection. By such design, MT CS call failure may beavoided and the call delay may also be reduced up to 10 seconds (e.g.,timer value of the timer T3440).

FIG. 3 illustrates an example scenario 300 under schemes in accordancewith implementations of the present disclosure. Scenario 300 involves aUE 310 and a network apparatus 320, which may be a part of a wirelesscommunication network (e.g., a Long Term Evolution (LTE) network, aLTE-Advanced network, a LTE-Advanced Pro network, a 5th Generation (5G)network, a New Radio (NR) network, an Internet of Things (IoT) networkor a Narrow Band Internet of Things (NB-IoT) network). In order toperform a NAS signaling procedure, UE 310 may need to establish a NASsignaling connection with network apparatus 320. UE 310 may beconfigured to initiate an attach procedure such as a combined EPS/IMSIattach procedure. After the attach procedure, a NAS signaling connectionmay be established between UE 310 and network apparatus 320. UE 310 maybe in a connected state or a connected mode.

UE 310 may be configured to initiate a NAS signaling procedure. UE 310may transmit a NAS message (e.g., a TAU request message without anactive flag) to network apparatus 320. After receiving the NAS message,network apparatus 320 may reject the request and transmit a NAS responsemessage (e.g., a TAU reject message) to UE 310. Network apparatus 320may indicate UE 310 to start a timer to control the established NASsignaling connection in the TAU reject message. After receiving the TAUreject message, UE 310 may further be configured to initiate a timerT3440. The timer value of the timer T3440 may be configured, for exampleand without limitation, 10 seconds. The timer T3440 may be configured tocontrol release of the signaling connection. Since there is no data fortransmission, UE 310 may initiate the timer T3440 to wait for release ofthe signaling connection initiated by network apparatus 320. If networkapparatus 320 does not release the signaling connection, UE 310 shouldlocally release the signaling connection.

Before expiration of the timer T3440, there may be a MT CS call coming.Network apparatus 320 may transmit a CS service notification message toinform UE 310 the incoming MT CS call. According to implementations ofthe present disclosure, after receiving the CS service notificationmessage, UE 310 may be configured to stop the timer T3440 and re-use theexisting NAS signaling connection to execute the CS service procedure.Specifically, UE 310 may be configured to perform a CSFB procedure tofallback to a CS service network to execute the CS service procedure.Accordingly, UE 310 may be able to take the MT CS call by using theexisting signaling connection. By such design, MT CS call failure may beavoided and the call delay may also be reduced up to 10 seconds (e.g.,timer value of the timer T3440).

FIG. 4 illustrates an example scenario 400 under schemes in accordancewith implementations of the present disclosure. Scenario 400 involves aUE 410 and a network apparatus 420, which may be a part of a wirelesscommunication network (e.g., a Long Term Evolution (LTE) network, aLTE-Advanced network, a LTE-Advanced Pro network, a 5th Generation (5G)network, a New Radio (NR) network, an Internet of Things (IoT) networkor a Narrow Band Internet of Things (NB-IoT) network). In order toperform a NAS signaling procedure, UE 410 may need to establish a NASsignaling connection with network apparatus 420. UE 410 may beconfigured to initiate an attach procedure such as a combined EPS/IMSIattach procedure. After the attach procedure, a NAS signaling connectionmay be established between UE 410 and network apparatus 420. UE 410 maybe in a connected state or a connected mode.

UE 410 may be configured to initiate a NAS signaling procedure. UE 410may transmit a NAS message (e.g., a detach request message) to networkapparatus 420. After receiving the NAS message, network apparatus 420may accept the request and transmit a NAS response message (e.g., adetach accept message) to UE 410. Network apparatus 420 may indicate UE410 to start a timer to control the established NAS signaling connectionin the detach accept message. After receiving the detach accept message,UE 410 may further be configured to initiate a timer T3440. The timervalue of the timer T3440 may be configured, for example and withoutlimitation, 10 seconds. The timer T3440 may be configured to controlrelease of the signaling connection. Since there is no data fortransmission, UE 410 may initiate the timer T3440 to wait for release ofthe signaling connection initiated by network apparatus 420. If networkapparatus 420 does not release the signaling connection, UE 410 shouldlocally release the signaling connection.

Before expiration of the timer T3440, there may be a MT CS call coming.Network apparatus 420 may transmit a CS service notification message toinform UE 410 the incoming MT CS call. According to implementations ofthe present disclosure, after receiving the CS service notificationmessage, UE 410 may be configured to stop the timer T3440 and re-use theexisting NAS signaling connection to execute the CS service procedure.Specifically, UE 410 may be configured to perform a CSFB procedure tofallback to a CS service network to execute the CS service procedure.Accordingly, UE 410 may be able to take the MT CS call by using theexisting signaling connection. By such design, MT CS call failure may beavoided and the call delay may also be reduced up to 10 seconds (e.g.,timer value of the timer T3440).

FIG. 5 illustrates an example scenario 500 under schemes in accordancewith implementations of the present disclosure. Scenario 500 involves aUE 510 and a network apparatus 520, which may be a part of a wirelesscommunication network (e.g., a Long Term Evolution (LTE) network, aLTE-Advanced network, a LTE-Advanced Pro network, a 5th Generation (5G)network, a New Radio (NR) network, an Internet of Things (IoT) networkor a Narrow Band Internet of Things (NB-IoT) network). In order toperform a NAS signaling procedure, UE 510 may need to establish a NASsignaling connection with network apparatus 520. UE 510 may beconfigured to initiate an attach procedure such as a combined EPS/IMSIattach procedure. After the attach procedure, a NAS signaling connectionmay be established between UE 510 and network apparatus 520. UE 510 maybe in a connected state or a connected mode.

UE 510 may be configured to initiate a NAS signaling procedure. UE 510may transmit a NAS message (e.g., a service request message) to networkapparatus 520. After receiving the NAS message, network apparatus 520may reject the request and transmit a NAS response message (e.g., aservice reject message) to UE 510. The service reject message mayfurther comprise a reject cause number for specifying the reason ofrejection. The reject cause number may comprise, for example and withoutlimitation, a reject cause #9, a reject cause #10, a reject cause #39 ora reject cause #40. Network apparatus 520 may indicate UE 510 to start atimer to control the established NAS signaling connection in the servicereject message. After receiving the service reject message, UE 510 mayfurther be configured to initiate a timer T3440. The timer value of thetimer T3440 may be configured, for example and without limitation, 10seconds. The timer T3440 may be configured to control release of thesignaling connection. Since there is no data for transmission, UE 510may initiate the timer T3440 to wait for release of the signalingconnection initiated by network apparatus 520. If network apparatus 520does not release the signaling connection, UE 510 should locally releasethe signaling connection.

Before expiration of the timer T3440, there may be a MT CS call coming.Network apparatus 520 may transmit a CS service notification message toinform UE 510 the incoming MT CS call. According to implementations ofthe present disclosure, after receiving the CS service notificationmessage, UE 510 may be configured to stop the timer T3440 and re-use theexisting NAS signaling connection to execute the CS service procedure.Specifically, UE 510 may be configured to perform a CSFB procedure tofallback to a CS service network to execute the CS service procedure.Accordingly, UE 510 may be able to take the MT CS call by using theexisting signaling connection. By such design, MT CS call failure may beavoided and the call delay may also be reduced up to 10 seconds (e.g.,timer value of the timer T3440).

In some implementations, before expiration of the timer T3440, there maybe a mobile-originated (MO) CS call initiated. Specifically, when thetimer T3440 is running, the UE may be operated by a user to initiate aMO CS call. The processor of the UE may receive a CS servicenotification which may be a MO CS call request. According toimplementations of the present disclosure, after receiving the MO CScall request, the UE may be configured to stop the timer T3440 andre-use the existing NAS signaling connection to execute the CS serviceprocedure. The UE may be configured to perform a CSFB procedure tofallback to a CS service network to execute the CS service procedure.Accordingly, the UE may be able to initiate the MO CS call by using theexisting signaling connection. By such design, MO CS call failure may beavoided and the call delay may also be reduced.

In some implementations, after the NAS signaling connection isestablished between the UE and the network apparatus, the UE may be inan evolved packet system mobility management (EMM)-connected mode. Whenthe UE transmits a NAS message or receives a NAS response message, theUE may move to an EMM-service-request-initiated state. In theEMM-service-request-initiated state, when the UE receives a CS servicenotification message from the network apparatus, the UE may beconfigured to stop the timer T3440 and re-use the existing NAS signalingconnection to execute the CS service procedure.

Illustrative Implementations

FIG. 6 illustrates an example communication apparatus 610 and an examplenetwork apparatus 620 in accordance with an implementation of thepresent disclosure. Each of communication apparatus 610 and networkapparatus 620 may perform various functions to implement schemes,techniques, processes and methods described herein pertaining toavoiding circuit-switched call drop with respect to user equipment andnetwork apparatus in wireless communications, including scenarios 200,300, 400 and 500 described above as well as process 700 described below.

Communication apparatus 610 may be a part of an electronic apparatus,which may be a user equipment (UE) such as a portable or mobileapparatus, a wearable apparatus, a wireless communication apparatus or acomputing apparatus. For instance, communication apparatus 610 may beimplemented in a smartphone, a smartwatch, a personal digital assistant,a digital camera, or a computing equipment such as a tablet computer, alaptop computer or a notebook computer. Communication apparatus 610 mayalso be a part of a machine type apparatus, which may be an IoT orNB-IoT apparatus such as an immobile or a stationary apparatus, a homeapparatus, a wire communication apparatus or a computing apparatus. Forinstance, communication apparatus 610 may be implemented in a smartthermostat, a smart fridge, a smart door lock, a wireless speaker or ahome control center. Alternatively, communication apparatus 610 may beimplemented in the form of one or more integrated-circuit (IC) chipssuch as, for example and without limitation, one or more single-coreprocessors, one or more multi-core processors, or one or morecomplex-instruction-set-computing (CISC) processors. Communicationapparatus 610 may include at least some of those components shown inFIG. 6 such as a processor 612, for example. communication apparatus 610may further include one or more other components not pertinent to theproposed scheme of the present disclosure (e.g., internal power supply,display device and/or user interface device), and, thus, suchcomponent(s) of communication apparatus 610 are neither shown in FIG. 6nor described below in the interest of simplicity and brevity.

Network apparatus 620 may be a part of an electronic apparatus, whichmay be a network node such as a base station, a small cell, a router ora gateway. For instance, network apparatus 620 may be implemented in aneNodeB in a LTE, LTE-Advanced or LTE-Advanced Pro network or in a gNB ina 5G, NR, IoT or NB-IoT network. Alternatively, network apparatus 620may be implemented in the form of one or more IC chips such as, forexample and without limitation, one or more single-core processors, oneor more multi-core processors, or one or more CISC processors. Networkapparatus 620 may include at least some of those components shown inFIG. 6 such as a processor 622, for example. Network apparatus 620 mayfurther include one or more other components not pertinent to theproposed scheme of the present disclosure (e.g., internal power supply,display device and/or user interface device), and, thus, suchcomponent(s) of network apparatus 620 are neither shown in FIG. 6 nordescribed below in the interest of simplicity and brevity.

In one aspect, each of processor 612 and processor 622 may beimplemented in the form of one or more single-core processors, one ormore multi-core processors, or one or more CISC processors. That is,even though a singular term “a processor” is used herein to refer toprocessor 612 and processor 622, each of processor 612 and processor 622may include multiple processors in some implementations and a singleprocessor in other implementations in accordance with the presentdisclosure. In another aspect, each of processor 612 and processor 622may be implemented in the form of hardware (and, optionally, firmware)with electronic components including, for example and withoutlimitation, one or more transistors, one or more diodes, one or morecapacitors, one or more resistors, one or more inductors, one or morememristors and/or one or more varactors that are configured and arrangedto achieve specific purposes in accordance with the present disclosure.In other words, in at least some implementations, each of processor 612and processor 622 is a special-purpose machine specifically designed,arranged and configured to perform specific tasks including powerconsumption reduction in a device (e.g., as represented by communicationapparatus 610) and a network (e.g., as represented by network apparatus620) in accordance with various implementations of the presentdisclosure.

In some implementations, communication apparatus 610 may also include atransceiver 616 coupled to processor 612 and capable of wirelesslytransmitting and receiving data. In some implementations, communicationapparatus 610 may further include a memory 614 coupled to processor 612and capable of being accessed by processor 612 and storing data therein.In some implementations, network apparatus 620 may also include atransceiver 626 coupled to processor 622 and capable of wirelesslytransmitting and receiving data. In some implementations, networkapparatus 620 may further include a memory 624 coupled to processor 622and capable of being accessed by processor 622 and storing data therein.Accordingly, communication apparatus 610 and network apparatus 620 maywirelessly communicate with each other via transceiver 616 andtransceiver 626, respectively. To aid better understanding, thefollowing description of the operations, functionalities andcapabilities of each of communication apparatus 610 and networkapparatus 620 is provided in the context of a mobile communicationenvironment in which communication apparatus 610 is implemented in or asa communication apparatus or a UE and network apparatus 620 isimplemented in or as a network node of a communication network.

In some implementations, communication apparatus 610 may need toestablish a NAS signaling connection with network apparatus 620.Processor 612 may be configured to initiate an attach procedure such asa combined EPS/IMSI attach procedure. After the attach procedure, a NASsignaling connection may be established between communication apparatus610 and network apparatus 620. Processor 612 may be in a connected stateor a connected mode.

In some implementations, processor 612 may be configured to initiate aNAS signaling procedure. Processor 612 may be configured to transmit aNAS message (e.g., a TAU request message, a detach request message or aservice request message) to network apparatus 620. After receiving theNAS message, processor 622 may transmit a NAS response message (e.g., aTAU accept message, a TAU reject message, a detach accept message or aservice reject message) to communication apparatus 610. Processor 622may be configured to indicate communication apparatus 610 to start atimer to control the established NAS signaling connection in the NASresponse message. After receiving the NAS response, processor 612 mayfurther be configured to initiate a timer T3440. The timer value of thetimer T3440 may be configured, for example and without limitation, 10seconds. Processor 612 may configure the timer T3440 to control releaseof the signaling connection. Since there is no data for transmission,processor 612 may initiate the timer T3440 to wait for release of thesignaling connection initiated by network apparatus 620. If networkapparatus 620 does not release the signaling connection, processor 612should locally release the signaling connection.

In some implementations, before expiration of the timer T3440, there maybe a MT CS call coming. Processor 622 may transmit a CS servicenotification message to inform communication apparatus 610 the incomingMT CS call. After receiving the CS service notification message,processor 612 may be configured to stop the timer T3440 and re-use theexisting NAS signaling connection to execute the CS service procedure.Specifically, processor 612 may be configured to perform a CSFBprocedure to fallback to a CS service network to execute the CS serviceprocedure. Accordingly, processor 612 may be able to take the MT CS callby using the existing signaling connection.

In some implementations, before expiration of the timer T3440, there maybe a MO CS call initiated. Specifically, when the timer T3440 isrunning, processor 612 may be configured to initiate a MO CS call inresponse to operations by a user. Processor 612 may receive a CS servicenotification which may be a MO CS call request. After receiving the MOCS call request, processor 612 may be configured to stop the timer T3440and re-use the existing NAS signaling connection to execute the CSservice procedure. Processor 612 may be configured to perform a CSFBprocedure to fallback to a CS service network to execute the CS serviceprocedure. Accordingly, processor 612 may be able to initiate the MO CScall by using the existing signaling connection.

In some implementations, after the NAS signaling connection isestablished between communication apparatus 610 and the networkapparatus 620, processor 612 may be in an evolved packet system mobilitymanagement (EMM)-connected mode. When processor 612 transmits a NASmessage or receives a NAS response message, processor 612 may move to anEMM-service-request-initiated state. In theEMM-service-request-initiated state, when processor 612 receives a CSservice notification message from the network apparatus, processor 612may be configured to stop the timer T3440 and re-use the existing NASsignaling connection to execute the CS service procedure.

Illustrative Processes

FIG. 7 illustrates an example process 700 in accordance with animplementation of the present disclosure. Process 700 may be an exampleimplementation of scenarios 200, 300, 400 and 500, whether partially orcompletely, with respect to avoiding circuit-switched call drop inaccordance with the present disclosure. Process 700 may represent anaspect of implementation of features of communication apparatus 610.Process 700 may include one or more operations, actions, or functions asillustrated by one or more of blocks 710, 720, 730, 740 and 750.Although illustrated as discrete blocks, various blocks of process 700may be divided into additional blocks, combined into fewer blocks, oreliminated, depending on the desired implementation. Moreover, theblocks of process 700 may executed in the order shown in FIG. 7 or,alternatively, in a different order. Process 700 may be implemented bycommunication apparatus 610 or any suitable UE or machine type devices.Solely for illustrative purposes and without limitation, process 700 isdescribed below in the context of communication apparatus 610. Process700 may begin at block 710.

At 710, process 700 may involve communication apparatus 610 transmittinga non-access stratum (NAS) message in a NAS signaling connection.Process 700 may proceed from 710 to 720.

At 720, process 700 may involve communication apparatus 610 receiving aNAS response message. Process 700 may proceed from 720 to 730.

At 730, process 700 may involve communication apparatus 610 initiating atimer to control the NAS signaling connection. Process 700 may proceedfrom 730 to 740.

At 740, process 700 may involve communication apparatus 610 receiving acircuit-switched (CS) service notification. Process 700 may proceed from740 to 750.

At 750, process 700 may involve communication apparatus 610 stopping thetimer and executing a CS service procedure.

In some implementations, process 700 may involve communication apparatus610 executing the CS service procedure by re-using the NAS signalingconnection.

In some implementations, the NAS message may comprise at least one of atracking area update (TAU) request message, a detach request message ora service request message. The NAS response message may comprise atleast one of a TAU accept message, a TAU reject message, a detach acceptmessage or a service reject message.

In some implementations, the timer to control the NAS signalingconnection may comprise T3440. The CS service notification may comprisea mobile-terminated (MT) CS call indication or a mobile-originated (MO)CS call request.

In some implementations, process 700 may involve communication apparatus610 performing a circuit-switched fallback (CSFB) procedure to executethe CS service procedure.

In some implementations, process 700 may involve communication apparatus610 releasing the NAS signaling connection in response to expiration ofthe timer.

In some implementations, process 700 may involve communication apparatus610 stopping the timer upon receiving the CS service notification in anevolved packet system mobility management(EMM)-service-request-initiated state.

Additional Notes

The herein-described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely examples, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

Further, with respect to the use of substantially any plural and/orsingular terms herein, those having skill in the art can translate fromthe plural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

Moreover, it will be understood by those skilled in the art that, ingeneral, terms used herein, and especially in the appended claims, e.g.,bodies of the appended claims, are generally intended as “open” terms,e.g., the term “including” should be interpreted as “including but notlimited to,” the term “having” should be interpreted as “having atleast,” the term “includes” should be interpreted as “includes but isnot limited to,” etc. It will be further understood by those within theart that if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to implementations containing only onesuch recitation, even when the same claim includes the introductoryphrases “one or more” or “at least one” and indefinite articles such as“a” or “an,” e.g., “a” and/or “an” should be interpreted to mean “atleast one” or “one or more;” the same holds true for the use of definitearticles used to introduce claim recitations. In addition, even if aspecific number of an introduced claim recitation is explicitly recited,those skilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number, e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations. Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention, e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc. In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention, e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc. It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

From the foregoing, it will be appreciated that various implementationsof the present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various implementations disclosed herein are notintended to be limiting, with the true scope and spirit being indicatedby the following claims.

What is claimed is:
 1. A method, comprising: transmitting, by aprocessor of an apparatus, a non-access stratum (NAS) message in a NASsignaling connection; receiving, by the processor, a NAS responsemessage; initiating, by the processor, a timer according to anindication in the NAS response message that instructs the processor toinitiate the timer to control the NAS signaling connection by releasingthe NAS signaling connection upon expiration of the timer; receiving, bythe processor, a circuit-switched (CS) service notification; andstopping, by the processor responsive to receiving the CS servicenotification, the timer before expiration of the timer to execute a CSservice procedure.
 2. The method of claim 1, wherein the executingcomprises executing the CS service procedure by re-using the NASsignaling connection.
 3. The method of claim 1, wherein the NAS messagecomprises at least one of a tracking area update (TAU) request message,a detach request message or a service request message.
 4. The method ofclaim 1, wherein the NAS response message comprises at least one of aTAU accept message, a TAU reject message, a detach accept message or aservice reject message.
 5. The method of claim 1, wherein the timer thatcontrols the NAS signaling connection comprises T3440.
 6. The method ofclaim 1, wherein the CS service notification comprises amobile-terminated (MT) CS call indication.
 7. The method of claim 1,wherein the CS service notification comprises a mobile-originated (MO)CS call request.
 8. The method of claim 1, further comprising:performing, by the processor, a circuit-switched fallback (CSFB)procedure to execute the CS service procedure.
 9. The method of claim 1,further comprising: releasing, by the processor, the NAS signalingconnection in response to expiration of the timer.
 10. The method ofclaim 1, wherein the stopping comprises stopping the timer uponreceiving the CS service notification in an evolved packet systemmobility management (EMM)-service-request-initiated state.
 11. Anapparatus, comprising: a transceiver capable of wirelessly communicatingwith a plurality of nodes of a wireless network; and a processorcommunicatively coupled to the transceiver, the processor capable of:transmitting, via the transceiver, a non-access stratum (NAS) message ina NAS signaling connection; receiving, via the transceiver, a NASresponse message; initiating a timer according to an indication in theNAS response message that instructs the processor to initiate the timerto control the NAS signaling connection by releasing the NAS signalingconnection upon expiration of the timer; receiving, via the transceiver,a circuit-switched (CS) service notification; and stopping, responsiveto receiving the CS service notification, the timer before expiration ofthe timer to execute a CS service procedure.
 12. The apparatus of claim11, wherein, in executing the CS service procedure, the processor iscapable of executing the CS service procedure by re-using the NASsignaling connection.
 13. The apparatus of claim 11, wherein the NASmessage comprises at least one of a tracking area update (TAU) requestmessage, a detach request message or a service request message.
 14. Theapparatus of claim 11, wherein the NAS response message comprises atleast one of a TAU accept message, a TAU reject message, a detach acceptmessage or a service reject message.
 15. The apparatus of claim 11,wherein the timer for controlling the NAS signaling connection comprisesT3440.
 16. The apparatus of claim 11, wherein the CS servicenotification comprises a mobile-terminated (MT) CS call indication. 17.The apparatus of claim 11, wherein the CS service notification comprisesa mobile-originated (MO) CS call request.
 18. The apparatus of claim 11,wherein the processor is further capable of: performing acircuit-switched fallback (CSFB) procedure to execute the CS serviceprocedure.
 19. The apparatus of claim 11, wherein the processor isfurther capable of: releasing the NAS signaling connection in responseto expiration of the timer.
 20. The apparatus of claim 11, wherein, instopping the timer, the processor is capable of stopping the timer uponreceiving the CS service notification in an evolved packet systemmobility management (EMM)-service-request-initiated state.